Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use a one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of system types or partnerships such as, General Packet Radio Service (GPRS), 3rd-Generation standards (3G), Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS), the 3rd Generation Partnership Project (3GPP), Evolution-Data Optimized (EV-DO), or Long Term Evolution (LTE).
Many wireless broadband network systems comprise base stations that serve mobile user devices. Within the wireless base station, the power amplifier (PA) is a key component. As more and more networks are deployed, there is an ever increasing pressure to improve the efficiency and lower the cost of these amplifiers. As power amplifiers become more power efficient, there is a corresponding decrease in the cost of the base station. For example, reduced thermal mitigation within the power amplifier reduces the need for cooling requirements such as fans, which, in turn, facilitates the use of smaller transistors. Furthermore, reduced power amplifier power reduces the cost to operate the base station as well.
One way to achieve efficiency improvements in power amplifiers is by allowing the constituent power transistors to operate closer to saturation. Such efficiency improvements, however, may come at the cost of reduced linearity of the amplifier that causes distortion inside the transmission band, which affects the ability of the amplifier to support high order modulation schemes, and outside of the transmission band, which affects the ability of the amplifier to comply with regulatory emission requirements.